let target = {};
let source = { a: { b: 3 }, sym: Symbol(1) };
Object.defineProperty(source, "innumerable", {
  value: "不可枚举属性",
  enumerable: false,
  writable: true,
});
Object.assign(target, source);
// source.innumerable = "good";
console.log(source);
console.log(target);
